It has been known a vehicle equipped with a control unit for controlling a rotary electric machine of an electric power steering apparatus, and a DC-DC converter that boosts a voltage of an electric power supplied from a battery and outputs the voltage boosted to the control unit. In a vehicle described in JP 5257389 B2 (hereinafter referred to as the patent literature 1), when a voltage of a battery is lowered due to the start of a starter to restart an engine after an idle reduction state of an automatic stop and start system, the voltage is boosted by the DC-DC converter and is outputted to the control unit. This restricts the control unit from being restarted or stopped due to the voltage of electric power supplied when the engine is restarted being lower than an operation guarantee voltage.
In the patent literature 1, when the DC-DC converter has an abnormality, it is difficult to output a voltage equal to or higher than the operation guarantee voltage when the engine is restarted. In such a case, the electric power steering apparatus will not function.
In the patent literature 1, the DC-DC converter is configured to boost the voltage supplied from the battery, and to output the voltage boosted to a control unit for an anti-block braking system and a navigation system, in addition to the control unit of the electric power steering apparatus. Therefore, the size of the DC-DC converter is large, and the DC-DC converter is accommodated in a housing that is separate from a housing of the control unit for the electric power steering apparatus. As such, it will be difficult to install the DC-DC converter to an installation space of a vehicle, which is usually limited. Further, in a case where plural housings are separately arranged, the manufacturing costs will increase.